1. Field of the Invention
The present invention relates to a network reconfiguration method, and more particularly to a network reconfiguration method and a router, by which if a network is separated due to shutdown of a communication link between relay units in the network, redundant routers reconfigure the separated networks as new subnets.
2. Description of the Related Art
Along with recent widespread use of an IT, a small-scale network such as a SOHO has been increased. Upon the configuration of the small-scale network, it is necessary to configure the network with a low cost and high reliability. For that purpose, a router is placed at a connection point with a WAN and the other portion is configured using a Layer2 network. On the other hand, the router or network configuration is set redundant to ensure a high reliability.
FIG. 1 shows an example of a network configuration that is redundant.
A network 300 is connected to a center side router 500 through a WAN 400. At this time, a router having a function of routing packets between the network 300 and the WAN 400 is designed as a dual-redundant system to ensure a high reliability; a master router 910 and a backup router 920 are provided. In the small-scale network, a relay unit for routing packets in the network 300 is configured using, for example, LS-SWs 91 and 92 as a Layer2 relay unit.
In addition, the redundant network is achieved using communication links 34 and 35 as indicated by the dotted lines of FIG. 1. As a result, a communication link 33 can be backed up even when being shut down.
However, the Layer2 relay unit (for example, a bridge) having a function of imparting redundancy to the network requires a higher device cost than a relay unit (for example, a hub) having no redundancy function. Thus, in the small-scale network configuration, it is desirable to use redundant routers only for a relay point with the WAN 400 and configure the other relay units in the network 300 using relay units (hub etc.) having no network redundancy function.
A VRRP (virtual router redundancy protocol) prescribed by the IETF (the Internet engineering task force) exemplifies a technique of controlling the above redundant routers. Japanese Unexamined Patent Application Publication No. 2002-232463 discloses a network configuration example based on the VRRP.
Further, an STP (spanning tree protocol) has been well known as another technique of controlling the redundant network.